Process for production of electroluminescent element and electroluminescent element

ABSTRACT

A process of producing an electroluminescent element is provided. The production process comprises repeating at least twice a step of forming an electroluminescent layer comprising a buffer layer and a luminescent layer by patterning using a photolithographic process, thereby producing an electroluminescent element comprising a patterned electroluminescent layer. The method includes the steps of forming a first pattern part comprising a first buffer layer as the lowermost layer, and coating a solution for forming a second buffer layer in a region including the first pattern part. The first buffer layer is immiscible with the solution for forming the second buffer layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 11/155,006,filed Jun. 16, 2005, now allowed, and claims the benefit under 35 USC119(a)-(d) of Japanese Application No. 2004-192024, filed Jun. 29, 2004,Japanese Application No. 2005-115469, filed Apr. 13, 2005 and JapaneseApplication No. 2005-155298, filed May 27, 2005, the entireties of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a process for producing anelectroluminescent (hereinafter referred to as “EL”) element comprisingan electroluminescent layer formed by photolithography, and anelectroluminescent element.

BACKGROUND OF THE INVENTION

EL elements cause holes and electrons, injected from opposed electrodes,to be combined within a luminescent layer to emit energy which excites afluorescent material within the luminescent layer to emit light of acolor corresponding to the fluorescent material, and have drawnattention as selfluminous planar display elements.

Among others, organic thin-film EL displays using an organic material asa luminescent material are expected to be applied to advertising orother low-cost simple displays that have high luminescence efficiency,for example, can realize high-brightness luminescence even in an appliedvoltage of a little less than 10 V, can emit light in a simple elementstructure, and can realize luminescence display of a specific pattern.

Such organic EL elements generally have a fundamental structurecomprising a first electrode layer and a second electrode layer stackedon top of each other through an organic EL layer, and, in general, thefirst electrode layer and the organic EL layer are patterned to form anelement which can realize different luminescent colors.

Patterning processes for organic EL elements are divided into a dryprocess in which a luminescent material is vacuum deposited through ashadow mask and a wet process in which a luminescent material dissolvedin an organic solvent is coated onto predetermined sites byphotolithography or ink jet printing. In these processes, patterning bythe wet process can eliminate the need to use an expensive vacuum systemand thus is advantageous, for example, in that the production cost canbe reduced. In particular, the photolithography can realizehigher-definition and higher-accuracy patterning as compared with theother methods and thus is expected to be applied to the preparation ofhigh-accuracy organic EL elements.

In general, however, among solvent-soluble organic EL materials used inthe wet process, only a very few organic EL materials can be renderedinsoluble in solvents by curing/crosslinking treatment. Therefore, thewet process poses a problem that, in patterning organic EL materialsdifferent from each other in color on an identical substrate, thealready formed organic EL layer is disadvantageously removed by thesolvent.

To overcome this problem, Japanese Patent Laid-Open No. 09-293589 A1(patent document 1) discloses that an organic EL element comprisingdifferent organic EL materials provided on an identical substrate can beprepared by forming an anode (a first electrode layer), an organic ELlayer, a cathode (a second electrode layer), and a protective layer inthat order on the whole area of a substrate, then providing aphotoresist on the protective layer, patterning the photoresist in adesired shape, and then continuously etching the cathode and the organicEL layer at their sites where the photoresist has been removed, byreactive ion etching (RIE).

Further, Japanese Patent Laid-Open No. 10-069981 A1 (patent document 2)discloses that organic EL layers different from each other in color canbe formed on an identical substrate by using materials prepared bydispersing organic EL materials and the link in an ultraviolet curableresin to render an already formed organic EL layer insoluble in thesolvent.

Furthermore, Japanese Patent Laid-Open No. 2001-237075 A1 (patentdocument 3) describes that redissolution of an already formed organicluminescent layer can be prevented by incorporating an organicluminescent material in a specific heat resistant resin and heat curingthe mixture.

In the above methods using a binder resin for fixing the organic ELmaterial and the like, however, since the organic EL material isdispersed in the resin, the luminescence efficiency or the service lifeis disadvantageously lowered. Further, it should be noted thatimpurities such as a reaction initiator and ions are present as amixture in the photosensitive resin used as the binder resin. Therefore,in some cases, the properties of the organic EL material and the likeare deteriorated by interaction between these impurities and the organicEL material.

For example, Japanese Patent Laid-Open No. 2002-170673 A1 (patentdocument 4) proposes a method shown in FIG. 4 as a method for forming aplurality of luminescent parts by photolithography.

At the outset, as shown in FIG. 4(a), a luminescent layer 42 is coatedonto a substrate 41 provided with an electrode, and, as shown in FIG.4(b), a photoresist layer 43 is stacked on the luminescent layer.Subsequently, as shown in FIG. 4(c), only a part where a firstluminescent part is to be formed is masked by a photomask 44, and thewhole photoresist layer except for the part covered by the photomask isexposed to ultraviolet light 45. The assembly is then developed with aphotoresist developing solution, followed by washing to remove thephotoresist layer 43 in its exposed area as shown in FIG. 4(d). Further,the assembly at its area where the photoresist layer has been removed toexpose the luminescent layer is removed by etching to provide anassembly shown in FIG. 4(e).

The above steps can be repeated three times to pattern three differentluminescent parts. Finally, peeling treatment is carried out with aphotoresist peeling liquid to expose three different luminescent parts42, 46, and 47 as shown in FIG. 4(n). Thereafter, for example, the stepof forming a second electrode layer on each of the luminescent parts iscarried out to prepare an EL element which emits light in a directionbelow the drawing.

In the above method, however, since the first luminescent part in itsend part a and the second luminescent part in its end part b areexposed, in coating other coating liquid for a luminescent layer later,disadvantageously, the patterned luminescent part at its end part iseluted in the coating liquid for a luminescent layer which is coatedlater, and, consequently, cross contamination and a change in filmthickness occurs, resulting in luminescence failure.

For example, Japanese Patent Laid-Open No. 2003-045656 A1 (patentdocument 5) proposes a method for providing a protective layer as shownin FIG. 5 as a method for preventing such cross contamination andpreventing pixels from getting narrower.

In this method, as shown in FIG. 5(a), a coating liquid for a firstluminescent layer is first spin coated onto the whole area of anassembly comprising a first electrode layer 52 patterned on a base 51and a buffer layer 53 provided on the first electrode layer 52. Thewhole area coated coating liquid for a first luminescent layer is driedand cured to form a first luminescent layer 54. A positive-workingphotoresist is coated on the whole area of the first luminescent layer54 to form a primary photoresist layer 55 (the step of forming aluminescent layer and a primary photoresist layer). Subsequently,ultraviolet light 57 is applied patternwise using a primary photomask 56so that a part corresponding to the first luminescent part is notexposed (FIG. 5(a)).

The primary photoresist layer 55 in its exposed part is developed with aphotoresist developing liquid followed by washing with water to removethe primary photoresist layer 55 in its exposed part (the step ofdeveloping primary photoresist layer). Upon further development with aluminescent layer developing liquid, the luminescent layer 54 only inits part not covered with the primary photoresist layer 55 is removed(FIG. 5(b), step of developing luminescent layer).

Further, as shown in FIG. 5(c), a positive-working photoresist isfurther coated onto the whole area thereof to form a secondaryphotoresist layer 55′ (the step of forming a secondary photoresistlayer).

A secondary photomask 56′ having a larger width than the primaryphotomask 56 for masking the primary photoresist layer shown in FIG.5(a) is used for exposure to ultraviolet light 57 (FIG. 5(d)). Thesecondary photoresist layer 55 in its exposed part is then developedwith a photoresist developing liquid and is washed with water to form asecondary photoresist layer 55′ (protective layer) covering the firstluminescent part 54′ and its end part a as shown in FIG. 5(e) (the stepof developing secondary photoresist layer).

Thus, in patterning one luminescent layer, carrying out the step ofdeveloping photoresist twice, that is, the step of developing a primaryphotoresist layer and the step of developing a secondary photoresistlayer, is advantageous in that, in such a state that the firstluminescent part 54′ in its end part a is covered by the photoresistlayer, the coating liquid for a second luminescent layer can be coatedfor next luminescent part formation, that is, second luminescent partformation. Therefore, even when the coating liquid for a secondluminescent layer is coated in FIG. 5(f), any problem such as crosscontamination does not occur.

The above steps are repeated three times, and the photoresist is thenpeeled off to form a first luminescent part 54′, a second luminescentpart 58′, and a third luminescent part 59′ (FIG. 5(1)). Finally, asshown in FIG. 5(m), a second electrode layer 60 is formed on theluminescent parts to produce an EL element which emitselectroluminescent light in a direction below the drawing.

In the above method for forming a secondary photoresist layer (aprotective layer) covering the end part a, the cross contamination andnarrowing of pixels can be prevented, but on the other hand, the numberof steps is large, posing a problem of production efficiency.

SUMMARY OF THE INVENTION

In view of the above problems of the prior art, the present inventionhas been made, and an object of the present invention is to provide aproduction process of an electroluminescent element, which, whileutilizing the advantages of photolithography, can prevent such anunfavorable phenomenon that the end part of the patterned part is elutedin a coating liquid coated after the formation of that part and,consequently, luminescent failure occurs as a result of crosscontamination and a change in layer thickness and can realize highproduction efficiency, and to provide an electroluminescent elementusing the same.

According to one aspect of the present invention, there is provided aprocess for producing an electroluminescent element, comprisingrepeating at least twice the step of forming an electroluminescent layercomprising a buffer layer and a luminescent layer by patterning using aphotolithographic process, thereby producing an electroluminescentelement comprising a patterned electroluminescent layer, the processcomprising the steps of: forming a first pattern part comprising a firstbuffer layer as the lowermost layer; and coating a solution for secondbuffer layer formation in a region including the first pattern part, thefirst buffer layer being immiscible with the solution for second bufferlayer formation.

In the present invention, the formed first buffer layer is not misciblewith the solution for second buffer layer formation. Therefore, afterpatterning an electroluminescent layer including the first buffer layerby photolithography, when the solution for second buffer layer formationis coated onto a region including the first pattern part, the end partof the already patterned first buffer layer is not eluted in thesolution for second buffer layer formation coated after the formation ofthat part. Therefore, luminescence failure derived from crosscontamination or a change in layer thickness does not occur.

Further, even in the case where a luminescent layer is further providedon the buffer layer, the material for luminescent layer formationselected is generally a material of which the solubility is differentfrom the material for buffer layer formation so that the material can becoated onto the buffer layer. Therefore, the end part of the alreadypatterned first luminescent layer is not eluted in the solution forsecond buffer layer formation coated later, and, in addition, the coatedsecond buffer layer functions as a protective layer, and, thus, elutionof the end part of the first luminescent part in the solution for secondluminescent layer formation coated later can be prevented.

In the prior art technique, when the step of forming anelectroluminescent layer by patterning using photolithography isrepeated twice or more, in the step of forming the first pattern partand the step of forming the second pattern part, in general, thematerial for luminescent layer formation in the first pattern part isidentical to or has the same solubility as the material luminescentlayer formation in the second pattern part, and the material for bufferlayer formation in the first pattern part is identical to or has thesame solubility as the material for buffer layer formation in the secondpattern part. Therefore, the solvent for the solution for firstluminescent layer formation is identical to or has the same solubilityas the solvent for the solution for second luminescent layer formation,and the solvent for the solution for first buffer layer formation isidentical to or has the same solubility as the solvent for the solutionfor second buffer layer formation. Therefore, when the end face of thealready patterned part is exposed, the step of forming the secondpattern part poses a problem that, in coating the solution for secondlowermost layer formation using a solvent which is identical to or hasthe same solubility as the solvent for the first coated solution, theend part of the lowermost layer in the pattern part is disadvantageouslyeluted in the solution. For example, in FIG. 6(a), when, in the step offorming a second pattern part, onto a base comprising a buffer layer 2,a luminescent layer 3, and a photoresist layer 4 formed in that order ona substrate 1 provided with an electrode in the step of forming a firstpattern part is coated a solution 6 (1) for buffer layer formation whichis the same as in the first buffer part, the end part of the firstbuffer part having the same solubility is disadvantageously dissolved inthe solution 6 (1) for buffer layer formation. Further, in FIG. 6(b),when, in the step of forming a second pattern part, onto a basecomprising a luminescent layer 3 and a photoresist layer 4 formed inthat order on a substrate 1 provided with an electrode in the step offorming a first pattern part is coated a solution 7 (1) for secondluminescent layer formation using a solvent having dissolving powersimilar to that of the solvent used in the first luminescent partformation, the end part of the first luminescent part having the samesolubility is disadvantageously dissolved in the solution 7 (1) forsecond luminescent layer formation. The dissolution of the end partposes a problem that luminescent failure occurs due to crosscontamination and a change in layer thickness.

The production process of an electroluminescent element according to thepresent invention, as shown in FIG. 1, includes the step of forming afirst pattern part 5 including a first buffer part 2 as the lowermostlayer (FIG. 1(a)) and the step of coating a solution 6 (1) for secondbuffer layer formation as the lowermost layer in a region including thefirst pattern part. In this process, a combination of the first bufferpart with the solution for second buffer layer formation is such thatthe first buffer part is not miscible with the solution for secondbuffer layer formation. Therefore, in the first stage in the step offorming a second pattern part, when a solution 6 (1) for second bufferlayer formation is coated in a region including the first pattern part 5so as to form the lowermost layer, the end part of the already patternedfirst buffer part 2 is not eluted in the solution 6 (1) for secondbuffer layer formation coated later (FIG. 1(b)). Further, even when aluminescent layer 3 is further provided, on the buffer layer 2, as anelectroluminescent layer formed by photolithography, since the materialfor luminescent layer formation selected is generally a material havinga solubility different from the material for buffer layer formation sothat the material can be stacked onto the buffer layer by coating, theend part of the already patterned first luminescent part 3 is not elutedin the later coated solution 6 (1) for second buffer layer formationand, in addition, the coated and dried second buffer layer 6 functionsas a protective layer, it is possible to prevent the end part of thefirst luminescent part from being eluted in the solution 7 (1) forsecond luminescent layer formation coated later (FIG. 1(c)).

Likewise, even when a photoresist part 4 is further provided on thefirst buffer part, since the material for the photoresist layer isgenerally selected by taking into consideration the solubility so thatthe photoresist layer can be stacked by coating on the buffer layer, theend part of the already patterned first photoresist layer 4 is noteluted in the solution 6 (1) for second buffer layer formation coatedlater and, in addition, the coated second buffer layer 6 functions as aprotective layer, it is possible to prevent the end part of the firstphotoresist layer 4 from being eluted in the solution for secondphotoresist layer formation coated later.

Accordingly, in the present invention, without the formation of a secondphotoresist layer (a protective layer) for covering the end part a ofthe patterned part as described in Japanese Patent Laid-Open No.2003-045656 A1, the occurrence of luminescence failure attributable tocross contamination or a change in layer thickness as a result ofelution of the end of the patterned part in the coating solution coatedafter the formation of that part can be prevented. That is, in thepresent invention, an element, which comprises a plurality of types ofhigh-definition pattern and exhibits good luminescence characteristics,can be prepared in a relatively easy and inexpensive manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one example of the productionprocess of an EL element according to the present invention;

FIG. 2 is a cross-sectional view showing one example of patterning usingphotolithography according to the present invention;

FIG. 3(a) is a diagram showing one example of an EL element usingphotolithography and FIG. 3(b) and FIG. 3(c) are cross-sectional viewsshowing one example of the conventional EL element;

FIG. 4 is a cross-sectional view showing one example of patterning usingphotolithography;

FIG. 5 is a cross-sectional view showing another example of patterningusing photolithography; and

FIG. 6 is a cross-sectional view showing one example of the conventionalproduction process of an EL element.

DETAILED DESCRIPTION OF THE INVENTION Definition

The production process of an electroluminescent element according to thepresent invention comprises repeating at least twice the step of formingan electroluminescent layer comprising a buffer layer and a luminescentlayer by patterning using a photolithographic process, thereby producingan electroluminescent element comprising a patterned electroluminescentlayer, the process comprising the steps of: forming a first pattern partcomprising a first buffer layer as the lowermost layer; and coating asolution for second buffer layer formation in a region including thefirst pattern part, the first buffer layer being immiscible with thesolution for second buffer layer formation.

The term “buffer layer” as used herein refers to a buffer layer formedat a predetermined position, and the term “pattern part” as used hereinrefers to a pattern part formed at a predetermined position. The firstpattern part may have a single layer structure of the first buffer layeror alternatively may have a multilayer structure comprising the firstbuffer layer as the lowermost layer. The term “buffer layer” as usedherein refers to a layer provided between an anode and a luminescentlayer or between a cathode and a luminescent layer and functions tofacilitate injection of charges into the luminescent layer and/orfunctions to flatten unevenness of electrodes or the like.

The term “luminescent layer” as used herein refers to a layer formed bycoating a solution for luminescent layer formation and drying thecoating, and the term “luminescent part” refers to a luminescent layerformed at a predetermined position.

Further, in “first, second” as used herein, in a process in whichpatterning is carried out twice or more by photolithography, the step inthe arbitrary number refers to a first step, and the step which iscarried out later than the first step is referred to as a second step.In this case, “later” is not limited to a time point immediately afterthe first step.

The expression “the first buffer layer is immiscible with the solutionfor second buffer layer formation” means that the formed first bufferlayer is not eluted in the solution for second buffer layer formation,that is, that the solubility of the first buffer layer in the solventcontained in the solution for second buffer layer formation is not morethan 0.001 (g/g-solvent) under conditions of 25° C. and 1 atm.

Production Process of Electroluminescent (EL) Element

In the present invention, the EL layer constituting the EL elementcomprises at least a buffer layer and a luminescent layer and may be incombination with other layers, for example, a hole transport layer, ahole injection layer, an electron transport layer, and an electroninjection layer.

When both the buffer layer and the luminescent layer are formed bypatterning using photolithography, the material for buffer layerformation selected is preferably insoluble in a photoresist solvent anda solvent for luminescent layer formation which will be described later.More preferably, the material for buffer layer formation selected isinsoluble in a photoresist peeling liquid.

On the other hand, when the luminescent layer is formed by vacuumdeposition or the like and the layer patterned by photolithography asthe EL layer is only a buffer layer, preferably, the material for bufferlayer formation selected is insoluble in a photoresist solvent and aphotoresist peeling liquid which will be described later.

The present invention comprises the step of forming a first pattern partincluding a first buffer layer as the lowermost layer and the step ofcoating a solution for second buffer layer formation as the lowermostlayer in a region including the first pattern part. In this case, acombination of the first buffer part with the solution for second bufferlayer formation is that the first buffer layer is immiscible with thesolution for second buffer layer formation, and the buffer layer isformed as the lowermost layer in the electroluminescent layer formed byphotolithography.

(1) Production Process in First Embodiment of Invention

In the first embodiment of the present invention, the first buffer layercan be rendered immiscible with the solution for second buffer layerformation by subjecting the buffer layer to curing treatment. The curingtreatment means that curing is carried out to such a level that thecured layer is substantially undissolvable or immiscible. This can bejudged using, as an index, such a state that, when the buffer layerafter curing is brought into contact with a solvent constituting thesolution for buffer layer formation for one min, the solubility is notmore than 0.001 (g/g-solvent) under conditions of 25° C. and 1 atm.

Preferably, the material for buffer layer formation comprises at least amaterial that is curable upon exposure to heat or radiation energy.Specific examples of curable materials include sol gel reactionsolutions, photocurable resins, and heat curable resins. The sol gelreaction solution refers to a reaction solution that gels upon curing.They are suitable as a binder in the material for buffer layerformation.

In the present invention, the first buffer layer is preferably formedusing a coating liquid for buffer layer formation, comprising at least ametal oxide and a heat- and/or photocurable binder. The reason for thisis that this buffer layer is good in charge injection efficiency and, inaddition, the buffer layer can be brought to a cured state and thus hasgood function as the buffer layer in the first embodiment. Such metaloxides include alkali metal oxides, alkaline earth metal oxides,transition metal oxides, and typical metal oxides.

In other embodiment of the present invention, the first buffer layer ispreferably formed using a coating liquid for buffer layer formation,comprising at least a photocatalyst and a heat- and/or photocurablebinder. The photocatalyst-containing layer formed in this case functionsas a buffer layer, and, in addition, the surface of thephotocatalyst-containing layer can be rendered hydrophilic byapplication of a radiation on the whole area after the formationthereof. Accordingly, when an EL layer is further formed by a wetprocess on the buffer layer, the solution for EL layer formation caneasily be coated and, even when the solution should be thinly coated,even coating can be realized.

For example, titanium dioxide (TiO₂), zinc oxide (ZnO), tin oxide(SnO₂), strontium titanate (SrTiO₃), tungsten oxide (WO₃), bismuth oxide(Bi₂O₃), and iron oxide (Fe₂O₃) known as semiconductors may be mentionedas the photocatalyst. They may be used either solely or as a mixture oftwo or more.

Among them, titanium dioxide is particularly suitable because of itshigh bandgap energy, chemically stable and nontoxic nature, and easyavailability. In the present invention, both anatase form of titaniumoxide and rutile form of titanium oxide may be used. However, the use ofanatase form of titanium oxide is preferred.

Further, preferably, the binder used in the present invention comprisesorganopolysiloxanes. Among organopolysiloxanes, those which have a mainskeleton having such high binding energy as not to be decomposed byphotoexcitation of the photocatalyst and contains an organic substituentdecomposable upon exposure to the action of a photocatalyst arepreferred, and examples thereof include (1) organopolysiloxanes which,through a sol gel reaction or the like, hydrolyze or polycondense achloro- or alkoxysilane or the like to exhibit great strength, and (2)organopolysiloxanes which are prepared by crosslinking reactive siliconeand has excellent water repellency and oil repellency. In the case oforganopolysiloxanes (1), they are preferably a hydrolyzed condensate orcohydrolyzed condensate of one or two or more silicon compoundsrepresented by formula Y_(n)SiX_((4-n)) wherein Y represents an alkyl,fluoroalkyl, vinyl, amino, phenyl, or epoxy group; X represents analkoxyl group, an acetyl group, or a halogen; and n is an integer of 0to 3. Here the number of carbon atoms of the group represented by Y ispreferably in the range of 1 to 20, and the alkoxy group represented byX is preferably a methoxy, ethoxy, propoxy, or butoxy group.

A fluoroalkyl-containing polysiloxane may also be used as the binder,and specific examples thereof include hydrolyzed condensate orcohydrolyzed condensate of one or two or more of variousfluoroalkylsilanes.

More specific examples thereof include methyltrichlorosilane,methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane,methyltriisopropoxysilane, methyltri-t-butoxysilane;ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane,ethyltriethoxysilane, ethyltriisopropoxysilane, ethyltri-t-butoxysilane;n-propyltrichlorosilane, n-propyltribromosilane,n-propyltrimethoxysilane, n-propyltriethoxysilane,n-propyltriisopropoxysilane, n-propyltri-t-butoxysilane;n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane,n-hexyltriethoxysilane, n-hexyltriisopropoxysilane,n-hexyltri-t-butoxysilane; n-decyltrichlorosilane,n-decyltribromosilane, n-decyltrimethoxysilane, n-decyltriethoxysilane,n-decyltriisopropoxysilane, n-decyltri-t-butoxysilane;n-octadecyltrichlorosilane, n-octadecyltribromosilane,n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane,n-octadecyltriisopropoxysilane, n-octadecyltri-t-butoxysilane;phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane,phenyltriethoxysilane, phenyltriisopropoxysilane,phenyltri-t-butoxysilane; tetrachlorosilane, tetrabromosilane,tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane,dimethoxydiethoxysilane; dimethyldichlorosilane, dimethyldibromosilane,dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldichlorosilane,diphenyldibromosilane, diphenyldimethoxysilane, diphenyldiethoxysilane;phenylmethyldichlorosilane, phenylmethyldibromosilane,phenylmethyldimethoxysilane, phenylmethyldiethoxysilane;trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane,triethoxyhydrosilane, triisopropoxyhydrosilane, tri-t-butoxyhydrosilane;vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane,vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltri-t-butoxysilane;trifluoropropyltrichlorosilane, trifluoropropyltribromosilane,trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane,trifluoropropyltriisopropoxysilane, trifluoropropyltri-t-butoxysilane;γ-glycidoxypropylmethyldimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-glycidoxypropyltriisopropoxysilane,γ-glycidoxypropyltri-t-butoxysilane;γ-methacryloxypropylmethyldimethoxysilane,γ-methacryloxypropylmethyldiethoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyltriethoxysilane,γ-methacryloxypropyltriisopropoxysilane,γ-methacryloxypropyltri-t-butoxysilane;γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,γ-aminopropyltriisopropoxysilane, γ-aminopropyltri-t-butoxysilane;γ-mercaptopropylmethyldimethoxysilane,γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane,γ-mercaptopropyltriethoxysilane, γ-mercaptopropyltriisopropoxysilane,γ-mercaptopropyltri-t-butoxysilane;β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltriethoxysilane; fluoroalkylsilanes whichare generally known as fluorosilane coupling agents and examples ofwhich are listed below; and their hydrolyzed condensates or cohydrolyzedcondensates; and their mixtures.

Fluoroalkylsilanes include CF₃(CF₂)₃CH₂CH₂Si(OCH₃)₃,CF₃(CF₂)₅CH₂CH₂Si(OCH₃)₃, CF₃(CF₂)₇CH₂CH₂Si(OCH₃)₃,CF₃(CF₂)₉CH₂CH₂Si(OCH₃)₃, (CF₃)₂CF(CF₂)₄CH₂CH₂Si(OCH₃)₃,(CF₃)₂CF(CF₂)₆CH₂CH₂Si(OCH₃)₃, (CF₃)₂CF(CF₂)₈CH₂CH₂Si(OCH₃)₃,CF₃(C₆H₄)C₂H₄Si(OCH₃)₃, CF₃(CF₂)₃(C₆H₄)C₂H₄Si(OCH₃)₃,CF₃(CF₂)₅(C₆H₄)C₂H₄Si(OCH₃)₃, CF₃(CF₂)₇(C₆H₄)C₂H₄Si(OCH₃)₃,CF₃(CF₂)₃CH₂CH₂SiCH₃(OCH₃)₂, CF₃(CF₂)₅CH₂CH₂SiCH₃(OCH₃)₂,CF₃(CF₂)₇CH₂CH₂SiCH₃(OCH₃)₂, CF₃(CF₂)₉CH₂CH₂SiCH₃(OCH₃)₂,(CF₃)₂CF(CF₂)₄CH₂CH₂SiCH₃(OCH₃)₂, (CF₃)₂CF(CF₂)₆CH₂CH₂SiCH₃(OCH₃)₂,(CF₃)₂CF(CF₂)₈CH₂CH₂SiCH₃(OCH₃)₂, CF₃(C₆H₄)C₂H₄SiCH₃(OCH₃)₂,CF₃(CF₂)₃(C₆H₄)C₂H₄SiCH₃(OCH₃)₂, CF₃(CF₂)₅(C₆H₄)C₂H₄SiCH₃(OCH₃)₂,CF₃(CF₂)₇(C₆H₄)C₂H₄SiCH₃(OCH₃)₂, CF₃(CF₂)₃CH₂CH₂Si(OCH₂CH₃)₃,CF₃(CF₂)₅CH₂CH₂Si(OCH₂CH₃)₃, CF₃(CF₂)₇CH₂CH₂Si(OCH₂CH₃)₃,CF₃(CF₂)₉CH₂CH₂Si(OCH₂CH₃)₃, and CF₃(CF₂)₇SO₂N(C₂H₅)C₂H₄CH₂Si(OCH₃)₃.

Among the above organopolysiloxanes, those containing a number offunctional groups which can be crosslink points such as an alkoxyl groupor a halogen are preferred from the viewpoint of forming a strong filmby crosslinking. Accordingly, in silicon compounds represented byformula Y_(n)SiX_((4-n)) wherein Y represents an alkyl, fluoroalkyl,vinyl, amino, phenyl, or epoxy group; X represents an alkoxyl group or ahalogen; and n is an integer of 0 to 3, n is preferably small,particularly n=0 is preferred.

Compounds having a skeleton represented by the following general formulamay be mentioned as organopolysiloxanes prepared by crosslinkingreactive silicone which are excellent in water repellency and oilrepellency.

wherein n is an integer of 2 or more; and R₁ and R₂ each represent asubstituted or unsubstituted alkyl, alkenyl, aryl or cyanoalkyl grouphaving 1 to 10 carbon atoms and not more than 40% in terms of molarratio of the whole thereof is accounted for by vinyl, phenyl, or aphenyl halide. Organopolysiloxanes wherein R₁ and R₂ represent a methylgroup are preferred because the surface energy is the lowest. Thecontent of the methyl group is preferably not less than 60% in terms ofmolar ratio. In the chain terminal or side chain, one or more reactivegroups such as hydroxyl group are contained in the molecular chain.

Further, a stable organosilicon compound, which does not cause anycrosslinking reaction, such as dimethylpolysiloxane, may be mixed incombination of the above organopolysiloxane in the binder.

The buffer layer may be formed, for example, by dispersing a metal oxidesuch as a photocatalyst and a binder optionally together with otheradditives in a solvent to prepare a solution for buffer layer formation,coating the solution for buffer layer formation onto a substrate with anelectrode layer formed thereon, and curing the coating. Preferredsolvents usable herein include alcoholic organic solvents such asethanol and isopropanol. Coating may be carried out by a conventionalmethod such as spin coating, spray coating, dip coating, roll coating,or bead coating. Curing treatment may be heat treatment. However, when aradiation curable component is contained as a binder, the buffer layermay be formed by applying a radiation for curing treatment.

The content of a metal oxide such as a photocatalyst in the solution forbuffer layer formation may be in the range of 5 to 60% by mass,preferably 20 to 40% by mass, based on the solid content. The thicknessof the buffer layer thus obtained is preferably in the range of 0.05 to10 μm.

In the first embodiment of the present invention, another method forsubjecting the buffer layer to curing treatment is to use a watersoluble solution for buffer layer formation. The solution preferablycontains a water- or alcohol-soluble or dispersible organic materialhaving a hydrophilic group in its molecule.

A hydroxyl group, a sulfonic acid group, or a carboxylic acid group maybe mentioned as the hydrophilic group. Suitable organic materials havinga hydrophilic group of this type include salts ofpoly-3,4-alkenedioxythiophenes with polystyrenesulfonic acid(hereinafter referred to as “PEDOT/PSS”) represented by formula

or their derivatives.

Further, in the present invention, the above materials having holeinjection properties in which a silane coupling agent has beenincorporated may be suitably used as the material for buffer layerformation. The addition of such a specific silane coupling agent canrealize curing of the hole injection layer through crosslinking and, atthe same time, enable the luminescence efficiency to be maintained orimproved.

Suitable silane coupling agents include materials represented by formula

wherein X represents OR wherein R represents an alkyl group; Yrepresents an epoxy or acryloyl group; and n is an integer of 0 to 2.Further, heating at a temperature of about 80 to 250° C., preferablyabout 100 to 200° C., can allow a silane coupling reaction to proceed tocrosslink and cure the hole injection layer.

In the present invention, as described above, since the buffer layer hasbeen cured, there is no fear of redissolution of the once formed bufferlayer in the solution for second buffer layer formation which is coatedafter that.

The content of the silane coupling agent in the solution for bufferlayer formation is preferably not less than 0.5% by weight. When thecontent of the silane coupling agent is not less than 0.5% by weight,the buffer layer can be more effectively cured.

(2) Production Process in Second Embodiment of Invention

In the second embodiment of the present invention, the first buffer partcan be rendered immiscible with the solution for second buffer layerformation by providing the step of varying the solubility of the bufferlayer. Here varying the solubility of the buffer layer is to vary thepolarity of a solvent in which the main component of the material forbuffer layer formation is dissolved or dispersed. When the solubility ofthe buffer layer is varied, the polarity of a solvent in which thebuffer part, which has already been formed as a buffer layer andpatterned, is soluble is different from the polarity of the solvent forthe solution for buffer layer formation are different from each other inpolarity. The level of a change in solubility may be such that, in thedifference in polarity, they are substantially neither dissolvable normiscible with each other. This can be judged using, as an index, such astate that, when the buffer layer after undergoing a change insolubility is brought into contact with a solvent constituting thesolution for buffer layer formation for one min, the solubility is notmore than 0.001 (g/g-solvent) under conditions of 25° C. and 1 atm.

Preferably, the material for buffer layer formation contains at least amaterial which undergoes a change in solubility upon exposure to heat orradiation energy. Specific examples of suitable materials of which thesolubility can be varied include materials for buffer layer formation inwhich a part or all of hydrophilic groups in a hydrophilic organicmaterial are converted to oleophilic groups and a part or all of theoleophilic groups are returned to hydrophilic groups by using heat orradiation energy.

The conversion of hydrophilic groups to oleophilic groups and theconversion of oleophilic groups to hydrophilic groups are not alwaysrequired for all the groups. For example, in the conversion ofhydrophilic groups to oleophilic groups, the conversion may be on theminimum level that solubility of a desired concentration or higher in anonaqueous general-purpose organic solvent can be maintained.Specifically, the convention may be such that a hydrophilic organicmaterial which is soluble or dispersible in water or an alcoholicsolvent is chemically treated to bring the solubility of the chemicallytreated material to not less than 0.5% by mass in a nonaqueousgeneral-purpose solvent such as toluene, xylene, ethyl acetate,cyclohexanone or the like.

On the other hand, reconversion of oleophilic groups to hydrophilicgroups may be on the minimum level that, in stacking a different layersuch as a luminescent layer by coating on the buffer layer, or in thecase of the formation of the first buffer layer followed by coating ofthe material for the formation of the adjacent buffer layer, the bufferlayer is not eluted in the solvent for coating. For example, the levelof reconversion may be such that the organic material buffer layer,which has been chemically converted so that the solubility in toluene,xylene, ethyl acetate, cyclohexanone or the like is not less than 0.5%by mass, is reconverted to such a form that is insoluble in ageneral-purpose solvent for coating such as toluene, xylene, ethylacetate, or cyclohexanone, or to such a hardly soluble form that isincompatible with the general-purpose solvent for coating upon contactfor a short period of time, and there is no need to fully return theorganic material to the original hydrophilic organic material.

From the viewpoint of forming a buffer layer with a chargeinjection/transport capability, the hydrophilic organic material ispreferably a material that is a hydrophilic hole transport material and,in use, is dispersible or dissolvable. Specific examples of holetransport materials include polyalkylthiophene derivatives, polyanilinederivatives, triphenylamine derivatives, triphenyldiamine derivatives,pyrazoline derivatives, arylamine derivatives, and stilbene derivatives.

Among them, salt-free sulfonic acid group, carboxylic acid group, andhydroxyl group are preferred as hydrophilic groups from the view pointof easiness on the conversion reaction.

Polystyrenesulfonic acid and its derivatives or organic materialscontaining them, or polythiophenesulfonic acid and its derivative ororganic materials containing them are preferred as the hydrophilicorganic material from the viewpoints of suitability for buffer layer,resistance to conversion treatment, easiness on purification, and cost.

Means for converting hydrophilic groups in the hydrophilic organicmaterial to oleophilic groups is preferably a protection reactionbecause, upon exposure to heat energy or a radiation, a part or thewhole of the oleophilic groups is returned to the hydrophilic groups.The protection reaction refers to a reaction which derivativeshydrophilic groups to temporarily introduce a protective group into thehydrophilic groups. The protection reaction is preferably at least onereaction selected from the group consisting of esterification,acetylation, tosylation, triphenylmethylation, alkylsilylation, andalkylcarbonylation.

Specifically, for example, a method may be adopted in which at least apart of sulfone groups or carboxyl groups is converted with achlorinating agent such as phosphorus pentaoxide or thionyl chloride toa sulfochloride group or a carbonylchloride group and an alcohol such asmethanol or ethanol is reacted with the chloride for esterification. Theabove reaction is one example of the conversion means, and the methodfor rendering the hole transport material in the present inventionoleophilic is not limited to the above method.

In the second embodiment of the present invention, an hydrophilicorganic material, such as a hole transport material, which has beenrendered oleophilic as described above, is dissolved or dispersed in anorganic solvent, for example, chloroform, methylene chloride,dichloroethane, tetrahydrofuran, acetone, or ethyl acetate, to prepare asolution for buffer layer formation. The concentration of thehydrophilic organic material such as a hole transport material in thesolution for buffer layer formation varies depending upon theingredients or composition of the hydrophilic organic material. Ingeneral, however, the hydrophilic organic material is dissolved ordispersed in the solvent to a concentration of not less than 0.1% bymass, preferably about 1 to 5% by mass. A coating film, that is, abuffer layer, is formed by coating the solution for buffer layerformation thus obtained onto the substrate and drying the coating.

The application of heat or radiation energy to the buffer layer thusformed causes the elimination of the protective group introduced by theprotection reaction, and the eliminated protective group is volatilized.Upon the elimination of the protective group, the solubility of theorganic material contained in the material for buffer layer formationwhich was oleophilic is rendered hydrophilic, and, consequently, theorganic material no longer is miscible with the solution for theoleophilic buffer layer formation.

Specifically, for example, upon the application of heat or radiationenergy, the ester bond is decomposed, and the esterified sulfone groupand/or carboxyl group is returned to a sulfone group or carboxyl groupin a free or salt form. The heat energy can be applied, for example, byheating at a temperature of about 200 to 220° C. for about 60 to 90 min.This heat treatment may be carried out simultaneously with heat dryingafter coating of the solution for buffer layer formation. Radiationsusable herein include, for example, ultraviolet light and electronbeams. Regarding irradiation conditions, for example, ultraviolet light(wavelength: not more than 400 nm) of about 200 to 250 mJ/cm² may beapplied. On the other hand, electron beams may be applied, for example,under conditions of not less than 500 kV and 35 mA.

The thickness of the buffer layer thus formed is generally about 100 to2000 angstroms.

The solvent used in the solution for buffer layer formation is notparticularly limited so far as the buffer material is dispersed ordissolved in the solvent. In the present invention, however, sincepatterning by photolithography is repeated twice or more to form asecond buffer layer in a region including the already patterned firstpattern part, the solvent for buffer layer formation should be a solventthat does not dissolve the photoresist layer or luminescent layer as theuppermost layer in the pattern part. The solvent for buffer layerformation usable in the present invention may be such that thesolubility of the resist material and the solubility of the material forluminescent layer formation satisfies the above solubility requirement.Any solvent satisfying the above requirement is usable, and, further,two or more solvents may be used as a mixture.

Electroluminescent (EL) Layer

In the present invention, the EL layer may comprise a hole transportlayer, a hole injection layer, an electron transport layer, an electroninjection layer and the like. However, the EL layer comprises at least abuffer layer and a luminescent layer that have been patterned. Thepatterning can realize an area color or a full color display elementand, further, can improve carrier injection balance in the EL element,and, thus, best use of the effect of the present invention can be made.

Specifically, in a preferred embodiment of the EL layer, a buffer layerpatterned by photolithography is provided as the EL layer on the firstelectrode layer, a luminescent layer patterned by photolithography isprovided as the EL layer on the buffer layer, and a second electrodelayer is further provided on the luminescent layer. Most preferred is afull-color EL element in which the luminescent layer exhibitsluminescence of three colors of RGB or the like formed by patterningusing photolithography three times.

The present invention is characterized in that, in patterning the ELlayer, patterning is carried out by photolithography. The other layersmay be formed by conventional methods. The photolithography is a methodin which a change in solubility of a film in its light exposed part uponlight irradiation is utilized to form any desired pattern according to alight irradiation pattern.

Unlike conventional vapor deposition conducted through a shadow mask,patterning using photolithography does not require the use of a vacuumdevice and the like and thus is advantageous in that the EL layer can bepatterned in an easy and inexpensive manner. Further, unlike patterningby ink jet printing, in photolithography, high-definition patterning canbe carried out, for example, without the need to conduct pretreatment ofthe base and to provide liquid-repellent convex parts between patterns.That is, the provision of the step of patterning at least one EL layerby photolithography enables a high-quality EL element having ahigh-definition pattern to be provided at low cost.

The steps in the production of an electroluminescent element accordingto the present invention will be described with reference to theaccompanying drawings.

In the step of forming a first pattern part including a first bufferpart as the lowermost layer, for example, as shown in FIG. 2(a), asolution for first buffer layer formation is coated onto a substrate 1having an electrode and optionally provided with a pattern alreadyformed without the use of photolithography so as to form a buffer layeras the lowermost layer, and the coating is dried to form a buffer layer2. As shown in FIG. 2(b), a luminescent layer 3 is further formed on thebuffer layer 2, and a photoresist layer 4 is stacked on the luminescentlayer 3. Subsequently, as shown in FIG. 2(c), a photomask 8 is masked onthe assembly only in its part where the first luminescent part is to beformed, and the other part is exposed to ultraviolet light 9.

The exposed assembly is developed with a photoresist developing solutionand is washed to remove the photoresist layer in its exposed part asshown in FIG. 2(d). As shown in FIG. 2(e), the part from which thephotoresist layer has been removed to expose the luminescent layer isfurther removed by etching to form a first pattern part 5 including thefirst buffer part 2 as the lowermost layer.

Next, the step of coating a solution for the formation of a secondbuffer layer as the lowermost layer in the region including the firstpattern part is carried out. In this step, for example, as shown in FIG.2(f), for forming the lowermost layer, the top of the substrate 1, thathas first pattern part 5, including the first buffer part 2 as thelowermost layer, provided on the substrate having the electrode andoptionally provided with the pattern already formed without the use ofphotolithography, is first coated with a solution 6 (1) for secondbuffer layer formation so as to include the region including the firstpattern part 5 and the region where a second pattern part is to beformed, generally on the whole area in a given range on the substrate.

The coated solution for buffer layer formation is dried in the samemanner as described above to form a second buffer layer 6. In this case,in order that a combination of the first buffer part with the solutionfor second buffer layer formation is that the first buffer part isimmiscible with the solution for second buffer layer formation, when thefirst embodiment is used, the step of curing the buffer layer ispreferably carried out in at least the step of forming the first patternpart including the first buffer part as the lowermost layer, and, thestep of curing the buffer layer is included after the formation of thefirst buffer layer and before patterning. When the step of forming thepattern part is carried out by n (wherein n is 2 or more)photolithography, the step of curing the buffer layer is preferablyincluded in the step of forming the pattern part using at least 1st to(n−1)th photolithography.

Further, in order that a combination of the first buffer part with thesolution for second buffer layer formation is such that the first bufferpart is immiscible with the solution for second buffer layer formation,in the second embodiment of the present invention, the step of varyingthe solubility of the buffer layer is preferably included after thecoating of the solution for second buffer layer formation in which atleast the solubility has been previously changed and before patterning.When, also in the step of forming the first buffer part, the solutionfor buffer layer formation in which the solubility has been previouslychanged as in the solution for second buffer layer formation, the stepof varying the solubility of the buffer layer should also be carried outin the step of forming the first pattern part. In this case, preferably,the step of varying the solubility of the buffer layer is included in astage after the formation of the first buffer layer and beforepatterning.

In the second embodiment, in all the steps of forming buffer parts usingthe solution for buffer layer formation in which the solubility has beenpreviously varied, the step of varying the solubility of the bufferlayer is preferably provided to vary the solubility and thus to returnthe buffer layer to such an original state that original charge transferand injection functions are provided.

Next, in the production of a full-color EL element, an embodiment of thestep of patterning a buffer layer and a luminescent layer by three-timephotolithography according to the production process of the presentinvention will be described.

At the outset, as described above, as shown in FIG. 2(a), a solution forfirst buffer layer formation is coated onto a substrate 1, having anelectrode and optionally provided with a pattern already formed withoutuse of photolithography, so as to form a buffer layer as the lowermostlayer, and the coating is then dried to form a buffer layer 2. In thefirst embodiment of the present invention, the buffer layer is cured byusing heat and/or radiation energy. On the other hand, in the secondembodiment of the present invention, when the solution for first bufferlayer formation used a material of which the solubility was previouslyvaried, the solubility of the buffer layer is varied by using heatand/or radiation energy.

As shown in FIG. 2(b), a luminescent layer 3 is further formed on thebuffer layer 2, and a photoresist layer 4 is stacked on the luminescentlayer 3. Subsequently, as shown in FIG. 2(c), a photomask 8 is masked onthe assembly only in its part where the first luminescent part is to beformed, and the other part is exposed to ultraviolet light 9.

The exposed assembly is developed with a photoresist developing solutionand is washed to remove the photoresist layer in its exposed part asshown in FIG. 2(d). As shown in FIG. 2(e), the part from which thephotoresist layer has been removed to expose the luminescent layer isfurther removed by etching to form a first pattern part 5 including thefirst buffer part 2 as the lowermost layer. Here, in the presentinvention, preferably, the step is transferred to the step of formingthe second pattern part in such a state that the photoresist layerlocated on the uppermost layer of the first pattern part remainsunpeeled. This is because, in the step of forming the second patternpart, in etching the luminescent layer and the buffer layer, thephotoresist layer functions to protect the first luminescent part so asto avoid the influence of the etching. Further, peeling off thephotoresist layers at a time at the final stage of the step of forming apattern part which is repeated twice or more is efficient.

Next, as shown in FIG. 2(f), in order to form the lowermost layer of thesecond pattern part, at the outset, a solution 6 (1) for second bufferlayer formation is coated so as to include the region including thefirst pattern part 5 and the region where the second pattern part is tobe formed. In the present invention, a combination of the first bufferpart with the solution for second buffer layer formation is that thefirst buffer part is immiscible with the solution for second bufferlayer formation. Therefore, when the solution 6 (1) for second bufferlayer formation is coated, the end part of the first pattern part 5 isnot eluted in the solution 6 (1) for second buffer layer formation.

Subsequently, the solution 6 (1) for buffer layer formation is dried,and, when the first embodiment is used, the buffer layer is cured byusing heat energy and/or a radiation. Further, when the secondembodiment is used, the solubility of the buffer layer is varied byusing heat energy and/or a radiation. Thus, the second buffer layer 6,which is insoluble in the same solution for buffer layer formation as inthe first buffer layer, is formed (FIG. 2(g)).

Subsequently, in the same manner as described above, the solution forsecond luminescent layer formation is coated to form a secondluminescent layer 7. In this case, even when the solution for secondluminescent layer formation is coated, since the second buffer layer 6functions as a protective layer, the end part of the first luminescentpart is not eluted in the solution for second luminescent layerformation. A positive working photoresist is coated on the whole area ofthe assembly to form a photoresist layer 4′ for a second pattern part(FIG. 2(h)).

Next, as shown in FIG. 2(i), in the same manner as described above, onlythe position where a second luminescent part is to be formed is maskedby a photomask 8, and ultraviolet light 9 is applied to positions otherthan the position where the second luminescent part is to be formed. Thephotoresist layer 4′ for a second pattern part is developed with aphotoresist developing solution and is washed, whereby the photoresistlayer 4′ for a second pattern part remains unremoved only in the partwhere the second luminescent part is to be formed (FIG. 2(j)).

As shown in FIG. 2(k), the part where the photoresist layer was removedto expose the luminescent layer is further removed by etching to form asecond pattern part 10 including the second buffer part 6 as thelowermost layer.

Next, the luminescent part for the third color is patterned. As shown inFIG. 2(1), in order to form the lowermost layer of the third patternpart, the solution 11 (1) for third buffer layer formation is firstcoated onto the substrate 1 so as to include the region including thefirst pattern part 5 and the second pattern part 10 and the region wherethe third pattern part is to be formed. In the present invention, acombination of the already formed first and second buffer parts with thesolution for third buffer layer formation is such that the alreadyformed first and second buffer parts are immiscible with the solutionfor third buffer layer formation. Therefore, when the solution 11 (1)for third buffer layer formation is coated, the end part of the firstpattern part 5 and the second pattern part 10 is not eluted in thesolution 11 (1) for third buffer layer formation.

The solution 11 (1) for third buffer layer formation is then dried, and,as with the step of forming the second pattern part, the buffer layer iscured by using heat energy and/or a radiation, or alternatively thesolubility of the buffer layer is varied, whereby a third buffer layer11 is formed (FIG. 2(m)).

The solution for third luminescent layer formation is then coated in thesame manner as described above to form a third luminescent layer 12. Inthis case, even when the solution for third luminescent layer formationis coated, since the second buffer layer 11 functions as a protectivelayer, the end part of the first luminescent part and the end part ofthe second luminescent part are not eluted in the solution for thirdluminescent layer formation. A positive working photoresist is coated onthe whole area of the assembly to form a photoresist layer 4″ for athird pattern part (FIG. 2(n)).

As shown in FIG. 2(o), in the same manner as described above, only theposition where the third luminescent part is to be formed is masked by aphotomask 8, and ultraviolet light 9 is applied to positions other thanthe position where the third luminescent part is to be formed. Thephotoresist layer 4″ for a third pattern part is developed with aphotoresist developing solution and is washed, whereby the photoresistlayer 4″ for a third pattern part remains unremoved only in the partwhere the third luminescent part is to be formed (FIG. 2(p)).

As shown in FIG. 2(q), the part where the photoresist layer was removedto expose the luminescent layer is further removed by etching to form athird pattern part 13 including the third luminescent part 12 with thethird buffer part 11 provided as the lowermost layer.

Finally, as shown in FIG. 2(r), each photoresist layer located on theuppermost layer is peeled off (step of peeling), and a second electrodelayer is formed on each of the exposed luminescent layers to produce anEL element which emits light downward in the drawing.

When the solution for the formation of a buffer layer as the lowermostlayer is coated, the buffer layer can be formed without causing adjacentbuffer layers to be miscible with each other. Further, since the bufferlayer as the lowermost layer functions as a protective layer for thealready formed pattern part, the adjacent luminescent layers are notmiscible with each other, and, in this way, an electroluminescent layercan be formed. Accordingly, in the electroluminescent element accordingto the present invention, without the need to form a secondaryphotoresist layer (a protective layer) for covering the end part of thepatterned part, the unfavorable phenomenon that the end part of thepatterned part is eluted in the later coated coating liquid resulting inluminescence failure due to cross contamination or a change in layerthickness can be prevented. Therefore, the electroluminescent elementaccording to the present invention is an element comprising a pluralityof types of high-definition patterns that have been formed relativelyeasily and at low cost.

Further, the EL element produced using the photolithographic process hasthe following features which are different from the features of ELelements produced by other processes.

At the outset, unlike other processes, in the photolithography, a filmis once coated on the whole area, and the film in its unnecessary partis removed by etching. Therefore, the EL element produced using thephotolithography is characterized by the shape 12 of the end part of theEL layer (see FIG. 3(a)). In the conventional processes such as vapordeposition and coating, as shown in FIG. 3(b), a slope of layerthickness occurs at the end part, and the width of the layer thicknessnonuniform region is wide. On the other hand, in the photolithography,since patterning is carried out by etching, as shown in FIG. 3(a), thelayer thickness at the end part is equal or similar to the layerthickness at the center part, that is, the width of the layer thicknessnonuniform region at the end part is advantageously not more than 15 μm,preferably not more than 10 μm, particularly preferably not more than 7μm. The term “layer thickness nonuniform region” refers to a regionwhere the layer thickness is not more than 90% of the average layerthickness of the flat part.

Further, for example, in the ink jet printing, a structure called apartition wall is necessary (FIG. 3(c)), and, thus, the EL layer isreceived within an insulating layer or the partition walls. On the otherhand, the photolithography is characterized in that none of the petitionwalls, the construct for aiding the patterning and the surface treatmentfor aiding the patterning are provided and that the end part of the ELlayer is formed on an insulating layer.

Next, individual members and the like used in each of the aboveproduction steps will be described.

(1) Photoresist

The photoresist used in the present invention may be either positiveworking type or negative working type and is not particularly limited.Preferably, however, the photoresist is soluble in a solvent, which doesnot dissolve the underlying layer, is coatable, and is insoluble in asolvent which is used in the formation of an EL layer such as a bufferlayer and a luminescent layer.

Specific examples of photoresists usable herein include novolak resinsand rubber+bisazide.

(2) Photoresist Solvent

In the present invention, preferably, the photoresist solvent used incoating the photoresist does not dissolve materials for EL layerformation such as a material for a buffer layer and a material for aluminescent layer from the viewpoints of preventing the EL layer such asa buffer layer and a luminescent layer in the formation of thephotoresist film and the photoresist material from being mixed ordissolved in each other and maintaining original luminescencecharacteristics. When this point is taken into consideration, thephotoresist solvent usable in the present invention preferably has asolubility in the material for EL layer formation such as a material fora buffer layer of not more than 0.001 (g/g-solvent), more preferably notmore than 0.0001 (g/g-solvent), under conditions of 25° C. and 1 atm. Ingeneral, in order to prevent mixing or dissolution in underlying layer,preferably, all the following cases satisfy the solubility requirement.

For example, photoresist solvents usable in the case where the materialfor buffer layer formation is dissolved in an aqueous solvent and theluminescent layer is dissolved in a nonpolar organic solvent such as anaromatic nonpolar organic solvent include: ketones including acetone andmethyl ethyl ketone; cellosolve acetates including propylene glycolmonoethyl ether acetate, propylene glycol monomethyl ether acetate,ethylene glycol monomethyl ether acetate, and ethylene glycol monoethylether acetate; cellosolves including propylene glycol monoethyl ether,propylene glycol monomethyl ether, ethylene glycol monomethyl ether, andethylene glycol monoethyl ether; alcohols including methanol, ethanol,1-butanol, 2-butanol, and cyclohexanol; ester solvents such as ethylacetate and butyl acetate; cyclohexanone; and decalin. Other solventsmay also be used so far as they satisfy the above requirements. A mixedsolvent composed of two or more solvents may also be used.

(3) Photoresist Developing Solution

The photoresist developing solution usable in the present invention isnot particularly limited so far as it does not dissolve the material forEL layer formation. Specifically, organic alkaline developing solutionscommonly used in the art may be used. Other developing solutions such asaqueous inorganic alkali solutions or aqueous solutions which candevelop the resist can be used. After the development of the resist,washing with water is preferred.

A developing solution in which the solubility of the material for ELlayer formation such as a luminescent layer material therein satisfiesthe solubility requirements may be used in the present invention.

(4) Photoresist Peeling Liquid

Further, the photoresist peeling liquid usable in the present inventionshould dissolve the photoresist layer rather than the dissolution of theEL layer, and the above photoresist solvent as such may be used. Whenthe positive working resist is used, a method may also be adopted inwhich, after UV exposure, the liquid mentioned as the resist developingsolution may be used for peeling.

Further, strongly alkaline aqueous solutions, solvents such asdimethylformamide, dimethylacetamide, dimethylsulfoxide,N-methyl-2-pyrrolidone, and mixtures thereof and commercially availableresist peeling liquids may also be used. After peeling of the resist,rinsing with 2-propanol or the like and further rinsing with water maybe carried out.

(5) Patterning by Photolithography

Regarding patterning by photolithography used in the present invention,specifically, when a positive working photoresist is used, at theoutset, the EL layer is formed on the whole area, a photoresist solutionprepared by dissolving the photoresist material in the photoresistsolvent is then coated onto the whole area thereof, and the coating isdried to form a photoresist layer. Next, the photoresist layer isexposed pattern-wise, and the photoresist in its exposed part isdeveloped with the above resist developing solution. Upon thedevelopment, only the photoresist in its unexposed part remainsunremoved. The EL layer in its part not covered by the photoresist isremoved to pattern the EL layer.

The method for forming the EL layer such as the buffer layer and theluminescent layer on the whole area may be the same as the formation ofthe conventional EL layer and is not particularly limited. Examplesthereof include vapor deposition and, in addition, electrodeposition,and coating methods using a melt, solution, or mixed liquid of thematerial, for example, spin coating, casting, dipping, bar coating,blade coating, roll coating, gravure coating, flexography, and spraycoating. Among others, wet film formation methods such as coating arepreferred from the viewpoint of utilizing an advantage that patterningcan be carried out without use of mask vapor deposition.

Methods for removing the EL layer in its part not covered by thephotoresist are divided into wet methods using solvents or the like anddry methods. In the present invention, dry etching (dry method)characterized by anisotropy is preferred. Accordingly, patterning byphotolithography is preferably carried out by coating a photoresist ontothe EL layer to be patterned, exposing and developing the coating topattern the photoresist, and then removing, by a dry etching process,the electroluminescent layer in its part where the photoresist has beenremoved. When the electroluminescent layer in its part where thephotoresist has been removed is removed by the dry etching process, theend part of the etching can be made sharper. Therefore, the width of thelayer thickness nonuniform region present in the end part of the patterncan be further reduced, and, consequently, higher-definition patterningcan be realized.

Reactive ion etching is preferred as the drying etching method. When thereactive ion etching is used, the organic material undergoes a chemicalreaction to give a compound having a low molecular weight that can beremoved from the substrate by volatilization or vaporization, and, thus,fabrication can be carried out with high etching accuracy in a shorttime.

In the dry etching, the use of oxygen as a simple substance oroxygen-containing gas is preferred. The use of oxygen as a simplesubstance or oxygen-containing gas can realize the decomposition andremoval of the organic luminescent layer by an oxidation reaction, canrealize the removal of unnecessary organic matter from the substrate,and can realize fabrication with high etching accuracy in a short time.Under the above conditions, a commonly used oxide transparent conductingfilm such as ITO is not etched. This is also advantageous in that thesurface of the electrode can be cleaned without sacrificing theelectrode characteristics.

Further, atmospheric pressure plasma is preferably used in the dryetching. When the atmospheric pressure plasma is used, dry etching whichusually requires the use of a vacuum apparatus can be carried out underthe atmospheric pressure and, thus, shortening of the treatment time anda reduction in cost can be realized. In this case, etching can utilize aphenomenon that the organic material is oxidatively decomposed by oxygenin the plasmatized air. The gas composition of a reaction atmosphere canbe regulated as desired by gas substitution and circulation.

(6) Luminescent Layer

In the present invention, the luminescent layer is preferably an organicluminescent layer and is generally composed mainly of an organicmaterial (a low molecular compound and a high molecular compound)capable of emitting fluorescence or phosphorescence and a dopant as anassistant.

In the present invention, when the luminescent layer on the buffer layeris formed by patterning using photolithography, a material, which isinsoluble in the above photoresist solvent and the solvent for thesolution for buffer layer formation, is preferably selected as thematerial for luminescent layer formation. More preferably, the materialfor luminescent layer formation is insoluble in the photoresist peelingliquid.

For example, the following materials may be mentioned as the materialfor luminescent layer formation usable in the present invention.

Coloring Matter Material

Coloring matter materials include, for example, cyclopentaminederivatives, tetraphenylbutadiene derivative compounds, triphenylaminederivatives, oxadiazole derivatives, pyrazoloquinoline derivatives,distyrylbenzene derivatives, distyrylarylene derivatives, pyrrolederivatives, thiophene ring compounds, pyridine ring compounds, perinonederivatives, perylene derivatives, oligothiophene derivatives,trifumarylamine derivatives, oxadiazole dimers, and pyrazoline dimers.

Metal Complex Material

Metal complex materials include, for example, quinolinol aluminumcomplexes, benzoquinolinol beryllium complexes, benzoxazolyl zinccomplexes, benzothiazole zinc complexes, azomethyl zinc complexes,porphyrin zinc complexes, europium complexes and the like, and metalcomplexes comprising Al, Zn, Be or the like or a rare earth metal suchas Tb, Eu, or Dy as a central metal having an oxadiazole, thiadiazole,phenylpyridine, phenylbenzimidazol, or quinoline structure as a ligand.

Polymeric Material

Polymeric materials include polyparaphenylenevinylene derivatives,polythiophene derivatives, polyparaphenylene derivatives, polysilanederivatives, polyacetylene derivatives, polyfluorene derivatives,polyvinylcarbazole derivatives, and materials prepared by polymerizingthe above coloring matter or metal complex luminescent materials.

Among the above luminescent materials, blue light emitting materialsinclude distyrylarylene derivatives, oxadiazole derivatives, and theirpolymers, polyvinylcarbazole derivatives, polyparaphenylene derivatives,and polyfluorene derivatives. Among them, polyvinylcarbazolederivatives, polyparaphenylene derivatives, polyfluorene derivatives andthe like as polymeric materials are preferred.

Green light emitting materials include quinacridone derivatives,coumarin derivatives, and their polymers, polyparaphenylenevinylenederivatives, and polyfluorene derivatives. Among them,polyparaphenylenevinylene derivatives, polyfluorene derivatives and thelike as polymeric materials are preferred.

Red light emitting materials include coumarin derivatives, thiophenering compounds, and their polymers, polyparaphenylenevinylenederivatives, polythiophene derivatives, and polyfluorene derivatives.Among them, polyparaphenylenevinylene derivatives, polythiophenederivatives, polyfluorene derivatives and the like as polymericmaterials are preferred.

Dopant Material

A dopant may be incorporated in the luminescent layer, for example, fromthe viewpoints of improving luminescence efficiency and varyingluminescence wavelength. Such dopants include, for example, perylenederivatives, coumarin derivatives, rubrene derivatives, quinacridonederivatives, squalium derivatives, porphyrin derivatives, styrylcoloring matters, tetracene derivatives, pyrazolone derivatives,decacyclene, and phenoxazone.

The thickness of the luminescent layer is generally about 20 to 2000angstroms.

When the luminescent layer is formed on the buffer layer byphotolithography, preferably, the solvent for the solution forluminescent layer formation prevents the buffer layer and the materialfor luminescent layer formation from being mixed or dissolved in eachother in the formation of the luminescent layer and does not dissolvethe buffer layer. For this reason, the solvent for the solution forluminescent layer formation may be such that the solubility of thebuffer layer in the solvent for the solution for luminescent layerformation satisfies the above solubility requirement.

For example, in the production process in the first embodiment, thebuffer layer is cured and thus is rendered insoluble in the solvent.Therefore, the solvent for the solution for luminescent layer formationis not particularly limited. Preferably, however, the first buffer layeris formed from a water soluble coating liquid for buffer layerformation, and the first luminescent layer is formed from a nonaqueouscoating liquid for luminescent layer formation.

In the production process in the second embodiment, the solvent used inthe solution for luminescent layer formation is not particularly limitedso far as the solvent satisfies the above solubility requirement thatthe buffer part after varying the solubility is less likely to bedissolved in the solvent, and, at the same time, the solubility of thematerial for luminescent layer formation in the solvent is high. Suchsolvents include organic solvents, for example, aromatic solventsincluding isomers of benzene, toluene and xylene and mixtures thereof,and isomers of mesitylene, tetralin, p-cymene, cumene, ethylbenzene,diethylbenzene, butylbenzene, chlorobenzene, and dichlorobenzene, andmixtures thereof, ether solvents including anisole, phenetole, butylphenyl ether, tetrahydrofuran, 2-butanone, 1,4-dioxane, diethyl ether,diisopropyl ether, diphenyl ether, dibenzyl ether, and diglyme, chlorosolvents such as dichloromethane, 1,1-dichloroethane,1,2-dichloroethane, trichloroethylene, tetrachloroethylene, chloroform,carbon tetrachloride, and 1-chloronaphthalene, and cyclohexanone. Othersolvents may also be used so far as the above requirements aresatisfied. Further, a mixed solvent composed of two or more solvents mayalso be used.

(7) Charge Transport/Injection Layer

In the EL element according to the present invention, a hole transportlayer, a hole injection layer, an electron transport layer, and anelectron injection layer may be provided. These layers are notparticularly limited so far as they are commonly used in conventional ELelement, for example, those described in Japanese Patent Laid-Open No.11-004011 A1.

(8) Substrate

The substrate is a support for an EL element and may be formed of, forexample, a flexible material or a rigid material. The substrate for anEL element used in the present invention is not particularly limited andmay be, for example, a glass or plastic sheet substrate used inconventional EL elements. The thickness of the substrate is generallyabout 0.1 to 2.0 mm.

(9) First and Second Electrodes

In the present invention, a first electrode is provided on thesubstrate, and a second electrode is provided on the EL layer. Theseelectrodes are an anode and a cathode. The electrode located in thedirection of takeout of light emitted from the EL layer should betransparent, and at least one of the first and second electrodes shouldbe formed of a transparent or semi-transparent material.

The electrode is formed of an electrically conductive material andpreferably has the lowest possible resistance. The electrode isgenerally formed of a metal material, or alternatively may be formed ofan organic compound or an inorganic compound. Further, the electrode maybe formed of a mixture of a plurality of materials.

The anode is preferably formed of an electrically conductive materialhaving a large work function from the viewpoint of easiness on holeinjection. Preferred anode materials include, for example, indium oxideand gold.

The cathode is preferably formed of an electrically conductive materialhaving a small work function from the viewpoint of easiness on electroninjection. Preferred cathode materials include, for example, magnesiumalloys (for example, Mg—Ag), aluminum alloys (for example, Al—Li, Al—Ca,and Al—Mg), metallic calcium and metals having a small work function.The thickness of each of the electrode layers is generally about 20 to1000 angstroms.

(10) Insulating Layer

In the EL element according to the present invention, in order to coverthe patterned edge part in the first electrode layer formed on thesubstrate and the nonluminescent part in the element and thus to preventshort-circuiting at the part unnecessary for luminescence, an insulatinglayer may be previously provided so that the insulating layer in itsluminescence part is in the form of an opening. This can reduce defectsattributable to short-circuiting of the element and can realize anelement that has a long service life and can stably emit light.

This insulating layer may be formed, for example, by forming a patternhaving a layer thickness of about 1 μm using an ultraviolet curableresin or the like. In the present invention, when the luminescent layeris patterned by dry etching, the insulating layer is preferablyresistant to dry etching. When the resistance to dry etching is low, alayer having a thickness of not less than 1 μm, for example, 1.5 to 10μm, is preferably formed to avoid a loss upon dry etching. Morepreferably, the layer is formed in a thickness of 2 to 5 μm.

The organic EL element according to the present invention may have, butnot limited to, the following constructions:

First electrode/buffer layer (hole injection layer/luminescentlayer)/second electrode;

First electrode/buffer layer (hole injection layer/luminescentlayer/electron injection layer)/second electrode;

First electrode/buffer layer (hole injection layer/electron blockinglayer/luminescent layer/electron injection layer)/second electrode; and

First electrode/buffer layer (hole injection layer/electron blockinglayer/luminescent layer/hole blocking layer/electron injectionlayer)/second electrode.

In the present invention, since the buffer layer is immiscible withsolutions for buffer layer formation, each layer may be formed by usingother solutions including solvents compatible with these solutions (forexample, a solution for electron injection layer formation and asolution for electron blocking layer formation). In particular, whenPEDOT/PPS is used as the material for hole injection layer formation,water or an alcoholic solvent is used in the coating liquid. Theindividual layers may be formed from coating liquids for each layerformation using water or alcoholic water-soluble solvents. For example,PEDOT/PPS is generally in a negatively charged state, and eachfunctional layer may be formed on the hole injection layer by adsorbinga positively charged water soluble material on the hole injection layerformed of PEDOT/PPS and optionally further adsorbing a negativelycharged material.

Regarding doping into the PEDOT/PPS hole injection layer, washing withan alcoholic or cellulosic solvent may be followed by doping into thehole injection layer to improve the luminescence efficiency of theorganic EL element.

The electron blocking layer provided between the hole injection layerand the luminescent layer may be formed by, after the hole injectionlayer formation, immersing the substrate in an aqueoustetramethoxysilane solution and drying the substrate. Further, theelectron blocking layer may also be formed by utilizing aself-organization method. Specifically, a method may be adopted in whichthe substrate is alternately immersed in aqueous polymer solutionsdifferent from each other in charge to alternately stack these polymerson top of each other by electrostatic adsorption effect (Nature 404, p.481 (2000) P. K. H. Ho et al.). When this self-organization method isutilized, the electrically conductive material and the semiconductormaterial can be alternately stacked and, thus, a stepwise gradient ofhole injection from the anode into the luminescent material can beprovided. This is attributable to the fact that a material having a widebandgap disposed at the interface of the luminescent layer functionsalso as an electron blocking layer.

The hole blocking layer is provided between the luminescent layer andthe electron injection layer. The hole blocking layer may be formed, forexample, by, after the luminescent layer formation, immersing thesubstrate in a solution of a water soluble resin of polystyrenesulfonicacid with metal ions (for example, sodium or lithium ions) coordinatedthereto. According to the present invention, after the patternedluminescent layer formation, the substrate can be immersed in the abovesolution to form a hole blocking layer on the whole area of thesubstrate.

EXAMPLES

The following examples further illustrate the present invention.However, it should be noted that the present invention is not limited tothese examples.

Example 1 Formation of First Buffer Layer

A patterned ITO substrate having a size of 6 in. square and a thickness1.1 mm was cleaned and was used as a base and a first electrode layer. Aphotocatalyst-containing solution for first buffer layer formationhaving the following composition was spin coated onto this substrate,and the coating was heated and dried at 150° C. for 10 min to allowhydrolysis and polycondensation to proceed and to cure the coating.Thus, a 200 angstrom-thick transparent photocatalyst-containing layerwas formed in which a photocatalyst had been firmly fixed inorganosiloxane.

Composition of Solution for First Buffer Layer Formation

-   -   Titanium dioxide (ST-K01, manufactured by Ishihara Sangyo Kaisha        Ltd.) 2 parts by mass    -   Organoalkoxysilane (TSL 8113, manufactured by Toshiba Silicone        Co., Ltd.) 0.4 part by mass    -   Fluoroalkylsilane (MF-160 E, manufactured by Tohchem Products        Corporation) 0.3 part by mass    -   isopropyl alcohol 3 parts by mass.

The buffer layer (photocatalyst-containing layer) was irradiated withultraviolet light at 70 mW/cm2 from a mercury vapor lamp (wavelength 365nm) for 50 sec. As a result, a hydrophilic surface having a contactangle with water of not more than 10 degrees could be obtained.

Formation of First Luminescent Layer

For first luminescent layer formation, one ml of a coating liquid as ared light emitting organic material (comprising 70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, 1 part by mass of adicyanomethylenepyran derivative, and 4900 parts by mass ofmonochlorobenzene) was placed dropwise on the buffer layer in its partcorresponding to the center part of the substrate to perform spincoating. Layer formation was carried out by holding at 2000 rpm for 10sec. As a result, the thickness of the layer thus formed was 800angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the firstluminescent part was exposed to ultraviolet light. After developmentwith a resist development liquid (NMD-3, manufactured by Tokyo OhkaKogyo Co., Ltd.) for 20 sec, the assembly was washed with water toremove the photoresist layer in its exposed parts. Post-baking wascarried out at 120° C. for 30 min. Thereafter, the buffer layer and theluminescent layer at their parts where the photoresist layer had beenremoved was removed by reactive ion etching with oxygen plasma. Thus, abase comprising a first pattern part where the first photoresist layerwas provided on the first luminescent part was obtained.

Formation of Second Buffer Layer

For second luminescent layer formation, the solution for second bufferlayer formation which was the same solution as used for first bufferlayer formation was provided. In the same manner as described above,this solution was coated on the base including the region of the firstpattern part, and the coating was heated and dried to allow hydrolysisand polycondensation to proceed and thus to perform curing. Thus, a 200angstrom-thick transparent photocatalyst-containing layer was formed inwhich a photocatalyst was firmly fixed in organosiloxane. In the abovecase, an identical solution for buffer layer formation was used for thefirst buffer layer and the second buffer layer. Since, in forming thesecond buffer layer, the first buffer layer was in an already curedstate, the first buffer layer was not eluted in the solution for secondbuffer layer formation.

Formation of Second Luminescent Layer

For second luminescent layer formation, one ml of a coating liquid as agreen light emitting organic material (comprising 70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, 1 part by mass ofcoumalin 6, and 4900 parts by mass of monochlorobenzene) was placeddropwise on the second buffer layer in its part corresponding to thecenter part of the substrate to perform spin coating. Layer formationwas carried out by holding at 2000 rpm for 10 sec. As a result, thethickness of the layer thus formed was 800 angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the firstluminescent part and the second luminescent part was exposed toultraviolet light. After development with a resist development liquid(NMD-3, manufactured by Tokyo Ohka Kogyo Co., Ltd.) for 20 sec, theassembly was washed with water to remove the photoresist in its exposedparts. Post-baking was carried out at 120° C. for 30 min. Thereafter,the buffer layer and the luminescent layer at their parts where thephotoresist layer had been removed were removed by reactive ion etchingwith oxygen plasma. Thus, a base comprising the first pattern part andthe second pattern part where the second photoresist layer was providedon the second luminescent part was obtained.

Formation of Third Buffer Layer

The same solution for buffer layer formation as the solution for firstbuffer layer formation was provided. In the same manner as describedabove, this solution was coated on the base including the region of thefirst and second pattern parts, and the coating was heated and dried toallow hydrolysis and polycondensation to proceed and thus to performcuring. Thus, a 200 angstrom-thick transparent photocatalyst-containinglayer was formed in which a photocatalyst was firmly fixed inorganosiloxane. In the above case, an identical solution for bufferlayer formation was used for the first, second and third buffer layers.Since, in forming the third buffer layer, the first and second bufferlayers were already in a cured state, upon coating of the solution forthird buffer layer formation, the first and second buffer layers werenot eluted in the solution for third buffer layer formation.

Formation of Third Luminescent Layer

For third luminescent layer formation, one ml of a coating liquid as ablue light emitting organic material (70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, one part by mass ofperylene, and 4900 parts by mass of monochlorobenzene) was placeddropwise on the buffer layer in its part corresponding to the centerpart of the substrate to perform spin coating. Layer formation wascarried out by holding at 2000 rpm for 10 sec. As a result, thethickness of the layer thus formed was 800 angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the first,second and third luminescent parts was exposed to ultraviolet light.After development with a resist development liquid (NMD-3, manufacturedby Tokyo Ohka Kogyo Co., Ltd.) for 20 sec, the assembly was washed withwater to remove the photoresist in its exposed parts. Post-baking wascarried out at 120° C. for 30 min. Thereafter, the buffer layer and theluminescent layer at their parts where the photoresist layer had beenremoved was removed by reactive ion etching with oxygen plasma. Thus, abase comprising the first, second, and third luminescence partsprotected by the photoresist was obtained. Thereafter, the photoresistwas fully removed by acetone to expose a patterned luminescent layer.

After drying at 100° C. for one hr, a 500 angstrom-thick secondelectrode layer of Ca was vapor deposited onto the base, and a 2500angstrom-thick protective layer of Ag was vapor deposited to prepare anEL element.

Example 2 Formation of Buffer Layer

Solid matter was separated from a dispersion ofpoly(styrenesulfonate)/poly(2,3-dihydrothieno[3,4-b]-1,4-dioxin(manufactured by Sigma-Aldrich Co.) in water by a supercentrifuge(Optima XL-100 K, manufactured by Beckman Coulter, Inc.) underconditions of 90,000 rpm×5 hr (20° C.), followed by filtration through afilter, predrying (150° C.×1 hr), grinding, and post-drying (underreduced pressure, 150° C.×12 hr) to give powder. A mixture of 100 partsby mass of the powder with 38 parts by mass of phosphorus pentaoxide wasboiled under reflux at 170° C. for 10 hr and was distilled, followed bydevelopment in tetrahydrofuran. Insolubles were removed by filtration,48 parts by mass of ethanol and 30 parts by mass of pyridine were addedto the filtrate, and the mixture was stirred under reflux for 24 hr foresterification. After the completion of the esterification, the reactionmixture was filtered to remove insolubles, the solvent was removed fromthe filtrate by distillation to give 63 parts by mass of a powderyesterification product. The esterification product was dissolved indichloroethane to a concentration of 1% by mass. The solution wasfiltered through a 0.5-μm filter to prepare a coating liquid.

Formation of First Buffer Layer

A patterned ITO substrate having a size of 6 in. square and a thickness1.1 mm was cleaned and was used as a base and a first electrode layer.The solution for buffer layer formation prepared above was spin coatedonto this substrate, and the coating was heated and dried at 150° C. forone hr. Thus, an 800 angstrom-thick transparent film was formed.

Formation of First Luminescent Layer

For first luminescent layer formation, one ml of a coating liquid as ared light emitting organic material (70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, 1 part by mass of adicyanomethylenepyran derivative, and 4900 parts by mass ofmonochlorobenzene) was placed dropwise on the buffer layer in its partcorresponding to the center part of the substrate to perform spincoating. Layer formation was carried out by holding at 2000 rpm for 10sec. As a result, the thickness of the layer thus formed was 800angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the firstluminescent part was exposed to ultraviolet light. After developmentwith a resist development liquid (NMD-3, manufactured by Tokyo OhkaKogyo Co., Ltd.) for 20 sec, the assembly was washed with water toremove the photoresist layer in its exposed parts. Post-baking wascarried out at 120° C. for 30 min. Thereafter, the buffer layer and theluminescent layer at their parts where the photoresist layer had beenremoved was removed by reactive ion etching with oxygen plasma. Thus, abase comprising a first pattern part where the first photoresist layerwas provided on the first luminescent part was obtained.

Formation of Second Buffer Layer

The same solution for buffer layer formation as the solution for firstbuffer layer formation was provided. In the same manner as describedabove, this solution was coated on the base including the region of thefirst pattern part, and the coating was heated and dried to form an 800angstrom-thick transparent film. In the above case, an identicalsolution for buffer layer formation was used for the first buffer layerand the second buffer layer. Since the first buffer layer was in such astate that the solubility had been changed, even when the solution forsecond buffer layer formation was coated, the first buffer layer was noteluted in the solution for second buffer layer formation.

Formation of Second Luminescent Layer

For second luminescent layer formation, one ml of a coating liquid as agreen light emitting organic material (comprising 70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, 1 part by mass ofcoumalin 6, and 4900 parts by mass of monochlorobenzene) was placeddropwise on the second buffer layer in its part corresponding to thecenter part of the substrate to perform spin coating. Layer formationwas carried out by holding at 2000 rpm for 10 sec. As a result, thethickness of the layer thus formed was 800 angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the firstluminescent part and the second luminescent part was exposed toultraviolet light. After development with a resist development liquid(NMD-3, manufactured by Tokyo Ohka Kogyo Co., Ltd.) for 20 sec, theassembly was washed with water to remove the photoresist layer in itsexposed parts. Post-baking was carried out at 120° C. for 30 min.Thereafter, the buffer layer and the luminescent layer at their partswhere the photoresist layer had been removed was removed by reactive ionetching with oxygen plasma. Thus, a base comprising the first patternpart and the second pattern part provided with the second photoresistlayer was obtained.

Formation of Third Buffer Layer

The same solution for buffer layer formation as the solution for firstbuffer layer formation was provided. In the same manner as describedabove, this solution was coated on the base including the region of thefirst and second pattern parts, and the coating was heated and dried toform an 800 angstrom-thick transparent film. In the above case, anidentical solution for buffer layer formation was used for the first,second and third buffer layers. Since, in forming the third bufferlayer, the first and second buffer layers were in such a state that thesolubility had been changed, upon coating of the solution for thirdbuffer layer formation, the first and second buffer layers were noteluted in the solution for third buffer layer formation.

Formation of Third Luminescent Layer

For third luminescent layer formation, one ml of a coating liquid as ablue light emitting organic material (70 parts by mass ofpolyvinylcarbazole, 30 parts by mass of oxadiazole, one part by mass ofperylene, and 4900 parts by mass of monochlorobenzene) was placeddropwise on the buffer layer in its part corresponding to the centerpart of the substrate to perform spin coating. Layer formation wascarried out by holding at 2000 rpm for 10 sec. As a result, thethickness of the layer thus formed was 800 angstroms.

A positive-working photoresist liquid (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) (2 ml) was placed dropwise at the center part ofthe base to perform spin coating. Layer formation was carried out byholding at 500 rpm for 10 sec and then at 2000 rpm for 20 sec. As aresult, the thickness of the layer reached about 1 μm. The coating wasprebaked at 80° C. for 30 min. Thereafter, the assembly, together withan exposure mask, was set in an alignment exposure system, and theluminescent layer at its parts to be removed except for the first,second and third luminescent parts was exposed to ultraviolet light.After development with a resist development liquid (NMD-3, manufacturedby Tokyo Ohka Kogyo Co., Ltd.) for 20 sec, the assembly was washed withwater to remove the photoresist layer in its exposed parts. Post-bakingwas carried out at 120° C. for 30 min. Thereafter, the buffer layer andthe luminescent layer at their parts where the photoresist layer hadbeen removed was removed by reactive ion etching with oxygen plasma.Thus, a base comprising the first, second, and third luminescence partsprotected by the photoresist was obtained. Thereafter, the photoresistwas fully removed by acetone to expose a patterned luminescent layer.

After drying at 100° C. for one hr, a 500 angstrom-thick secondelectrode layer of Ca was vapor deposited onto the base, and a 2500angstrom-thick protective layer of Ag was vapor deposited to prepare anEL element.

Evaluation of Luminescence Characteristics of EL Element

The ITO electrode side was connected to a positive electrode, and the Agelectrode side was connected to a negative electrode, and a directcurrent was applied through a source meter. In Examples 1 and 2,luminescence was observed from each of the first, second, and thirdluminescent parts upon the application of 10 V.

Results of Evaluation

In Examples 1 and 2, without the formation of a secondary photoresistlayer (protective layer) for covering the end part a of the patternedpart, the elution of the end part of the patterned part in the coatingliquid coated later to cause luminescence failure as a result of crosscontamination and a change in layer thickness can be prevented, and,thus, an element with a plurality of types of high-definition patternsformed therein could be formed in a relatively easy and inexpensivemanner.

Example 3 Preparation of Solution for Buffer Layer Formation

γ-Glycidoxypropyltrimethoxysilane having a glycido group (—CHOCH₂) as afunctional group (TSL 8350, manufactured by Toshiba Silicone Co., Ltd.)was added to an aqueous solution of PEDOT/PPS (Baytron P, manufacturedby Bayer) represented by the above formula in proportions on a PEDOT/PPSsolid basis as shown in Table 1 below to prepare a solution for bufferlayer formation.

Water Resistance Test

The solution for buffer layer formation thus obtained was spin coatedonto a glass substrate to form a 1000 angstrom-thick coating on a drybasis, and the coating was heat treated on a hot plate under conditionsof 100° C.×10 min for crosslinking curing. Subsequently, the glasssubstrate with the coating formed thereon was immersed in 100 g of waterto visually evaluate the state of coating.

Measurement of Luminescence Efficiency

Indium tin oxide (ITO) was vapor deposited onto a transparent glasssubstrate to form a first electrode. Subsequently, the solution forbuffer layer formation prepared above was spin coated onto the firstelectrode to form a 1000 angstrom-thick layer on a dry basis onto thewhole area of the first electrode, and the coating was heat treated on ahot plate under conditions of 100° C.×10 min to perform crosslinkingcuring, whereby a first buffer layer was formed.

Next, a 1 wt % xylene solution of a poly-p-phenylenevinylene derivative(hereinafter abbreviated to “MEH-PPV”) represented by formula

was prepared as a solution for luminescent layer formation. The solutionfor luminescent layer formation was spin coated onto the whole area ofthe first buffer layer to form a first luminescent layer having athickness of 1000 angstrom on a dry basis. Thus, a first EL layercomprising a first hole injection layer and a first luminescent layerwas formed.

A second electrode was formed on the first EL layer by vapor depositingcalcium to a layer thickness of 1000 angstrom.

In the EL element thus obtained, the first electrode was connected as apositive electrode to a source meter, and the second electrode wasconnected as a negative electrode to the source meter, followed by theapplication of a direct current.

The current value as a function of the applied voltage was measured witha source meter, and the brightness of the organic EL element as afunction of the applied voltage was measured with a luminance meter.Here the brightness per unit area as a function of the applied voltagewas calculated as luminescence efficiency.

Further, the maximum luminescence efficiency of the EL element wascalculated by presuming the maximum luminescence efficiency, when onlyPEDOT/PPS was used as a material for buffer layer formation, to be 1.

The results were as summarized in Table 1.

Example 4

An EL element was prepared in the same manner as in Example 3, exceptthat, in the solution for buffer layer formation,3-acryloxypropyltrimethoxysilane containing an acryloyl group (—CH═CH₂)as a functional group (KBM 5103, manufactured by Shin-Etsu Silicone) wasadded in proportions on a PEDOT/PPS solid basis as indicated in Table 1.

Comparative Example 1

An EL element was prepared in the same manner as in Example 3, exceptthat, in the solution for buffer layer formation, only PEDOT/PPS wasused.

Comparative Example 2

An EL element was prepared in the same manner as in Example 3, exceptthat, in the solution for buffer layer formation,γ-methacryloxypropyltrimethoxysilane containing a methacryloxy group(—CCH₃═CH₂) as a functional group (TSL 8370, manufactured by ToshibaSilicone Co., Ltd.) was added in proportions on a PEDOT/PPS solid basisas indicated in Table 1.

Comparative Example 3

An EL element was prepared in the same manner as in Example 3, exceptthat, in the solution for buffer layer formation,N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane containing an amino group(—NH₂) as a functional group (TSL 8340, manufactured by Toshiba SiliconeCo., Ltd.) was added in proportions on a PEDOT/PPS solid basis asindicated in Table 1.

Comparative Example 4

An EL element was prepared in the same manner as in Example 3, exceptthat, in the solution for buffer layer formation,γ-mercaptopropyltrimethoxysilane (KBM 803, manufactured by The Shin-EtsuChemical Co., Ltd.) containing a mercapto group (—SH) as a functionalgroup was added in proportions on a PEDOT/PPS solid basis as indicatedin Table 1.

The EL elements of Example 4 and Comparative Examples 1 to 4 were alsoevaluated in the same manner as in Example 3. The results were assummarized in Table 1 below. TABLE 1 Coupling agent Addition Maximumamount, Solubil- Pattern- luminescent Functional group wt % ity abilityefficiency Ex. 3 Glycido group 0.1 x x 1.00 1 ∘ ∘ 1.10 5 ∘ ∘ 1.2 10 ∘ ∘1.0 50 ∘ ∘ 1.0 100 ∘ ∘ 0.5 Ex. 4 Acryloyl group 0.1 x x 1.0 1 ∘ ∘ 1.05 5∘ ∘ 1.1 10 ∘ ∘ 1.0 50 ∘ ∘ 1.0 100 ∘ ∘ 0.6 Comp. Not added 0 x x 1.0 Ex.1 Comp. γ-methacryloxy 0.1 x x 1.0 Ex. 2 group 1 x x 1.0 5 x x 1.0 10 xx 1.0 50 x x 0.5 100 x x 0.3 Comp. Amino group 0.1 x x 1.0 Ex. 3 1 x x1.0 5 x x 1.0 10 x x 1.0 50 x x 0.6 100 x x 0.5 Comp. Mercapto group 0.1x x 1.0 Ex. 4 1 x x 1.0 5 x x 1.0 10 x x 1.0 50 x x 0.4 100 x x 0.3

Patterning of EL Layer

A first electrode was formed by vapor depositing indium tin oxide (ITO)on a transparent glass substrate. Subsequently, the solution for bufferlayer formation of each of Examples 1 and 2 and Comparative Examples 1to 3 was spin coated onto the whole area of the first electrode to forma coating having a thickness of 800 angstroms on a dry basis, and thecoating was heat treated on a hot plate under conditions of 100° C.×10min to perform crosslinking curing treatment, whereby a first bufferlayer was formed.

The solution for luminescent layer formation used in Example 3 was spincoated onto the whole area of the first buffer to form a firstluminescent layer having a thickness of 1000 angstroms on a dry basis.Thus, a first EL layer comprising a first hole injection layer and afirst luminescent layer was formed.

Next, a positive-working photoresist (OFPR-800, manufactured by TokyoOhka Kogyo Co., Ltd.) was spin coated onto the whole area of the firstluminescent layer to form a coating having a thickness of 1 μm on a drybasis, and the coating was dried to form a first photoresist layer.

Subsequently, ultraviolet light was applied by an alignment exposuresystem through a photomask (line width (light shielding part) 85 μm,space width (light transmission part) 215 μm) in which the lightshielding part corresponded to the first luminescent layer, and thephotoresist in the exposed area was removed by a resist developingliquid (NMD-3, manufactured by Tokyo Ohka Kogyo Co., Ltd.).

Thereafter, dry etching was carried out with an atmospheric-pressureplasma device to remove the first EL layer part from which thephotoresist had been removed, whereby the first EL layer was patterned.

Subsequently, a second buffer layer, a second luminescent layer, and asecond photoresist layer were formed on the dry-etched organic ELelement without separating the remaining photoresist in the same manneras in the formation of the first EL layer.

Next, the same photomask as used above was disposed at a position whichhad been shifted by one pitch (100 μm) relative to the substrate,followed by exposure and development in the same manner as describedabove to remove the photoresist. The second EL layer part from which thephotoresist had been removed was then removed to pattern the second ELlayer.

Subsequently, a third buffer layer, a third luminescent layer, and athird photoresist layer were formed on the dry-etched EL element withoutseparating the remaining photoresist in the same manner as in theformation of the first EL layer.

Next, the same photomask as used above was disposed at a position whichhad been shifted by two pitches (200 μm) relative to the substrate,followed by exposure and development in the same manner as describedabove to remove the photoresist. The third EL layer part from which thephotoresist had been removed was then removed to pattern the third ELlayer.

The substrate on which the EL layers had been formed was observed undera microscope, and, as a result, it was found that, in the pattern, theline width and the space width were 85 μm and 15 μm, respectively.

The photoresist in the unexposed area remaining on the EL layer wasimmersed in a resist solvent for 10 min to fully remove only the resistpart, whereby a substrate provided with a patterned EL layer wasprovided.

For examining patterning, the level of the patternability of the linepattern part was observed under a fluorescence optical microscope. Theresults were as summarized in Table 1.

Formation of Intermediate Layer

Example 5

A buffer layer was formed in the same manner as in Example 3, exceptthat, in the coating liquid for hole injection layer formation used inExample 3, the content of γ-glycidoxypropyltrimethoxysilane containing aglycido group (—CHOCH₂) as a functional group (TSL 8350, manufactured byToshiba Silicone Co., Ltd.) was 5% by weight.

Subsequently, the substrate with a buffer layer formed thereon wasimmersed in an aqueous tetramethoxysilane (KBM-04, manufactured by TheShin-Etsu Chemical Co., Ltd.) solution for 5 min, and the substrate wasthen washed with ion exchanged water. This substrate was dried on a hotplate under conditions of 110° C.×30 min to form an intermediate layer(an electron blocking layer).

After the formation of the intermediate layer, the buffer layer wasinspected by microscopic observation and layer thickness measurement. Asa result, no change in layer thickness was observed.

Next, the same solution for luminescent layer formation as used inExample 3 was provided, and, in the same manner as in Example 3, aluminescent layer was formed on the intermediate layer to form an ELlayer comprising a hole injection layer, an intermediate layer, and aluminescent layer on the substrate.

Comparative Example 5

The same solution for buffer layer formation as in Comparative Example 1was provided, and the procedure of Comparative Example 1 was repeated toform a buffer layer. Subsequently, the substrate with a buffer layerformed thereon was immersed in an aqueous tetramethoxysilane (KBM-04,manufactured by The Shin-Etsu Chemical Co., Ltd.) solution for 5 min,and, thereafter, the substrate was washed with ion exchanged water. Thissubstrate was dried on a hot plate under conditions of 130° C.×30 min toform an intermediate layer (electron blocking layer).

After the formation of the intermediate layer, the buffer layer wasobserved by microscopic observation and layer thickness measurement. Asa result, it was found that the buffer layer disadvantageouslydisappeared.

Next, the same solution for luminescent layer formation as used inExample 3 was provided, and the procedure of Example 3 was repeated toform a luminescent layer on the intermediate layer.

A second electrode was formed on each EL layer formed in Example 5 andComparative Example 5 by vapor depositing calcium to a layer thicknessof 1000 angstroms. Further, silver was vapor deposited to a thickness of2000 angstroms as an oxide protective film onto the second electrode toprepare an EL element.

In the EL element thus prepared, the first electrode was connected as apositive electrode to a source meter, and the second electrode wasconnected as a negative electrode to the source meter, and a directcurrent was applied.

The current value as a function of the applied voltage was measured witha source meter, and the brightness of the organic EL element as afunction of the applied voltage was measured with a luminance meter.Here the brightness per unit area as a function of the applied voltagewas calculated as luminescence efficiency.

Further, the maximum luminescence efficiency of the EL element wascalculated by presuming the maximum luminescence efficiency, when onlyPEDOT/PPS was used as a material for buffer layer formation, to be 1.

The results were as summarized in Table 2. The organic EL element inExample 6 is shown in comparison with the organic EL element in Example3 which has the same layer construction as the organic EL element inExample 6 except that no intermediate layer was provided (the amount ofγ-glycidoxypropyltrimethoxysilane added being 5% by weight). The ELelement in Comparative Example 5 is shown in comparison with the ELelement in Comparative Example 1 which has the same layer constructionas the EL element in Comparative Example 5, except that no intermediatelayer was provided. TABLE 2 Intermediate Maximum luminescence Couplingagent layer efficiency Ex. 3 Glycido group Not provided 1.2 Ex. 6Glycido group Provided 1.5 Comp. Ex. 1 Not used Not provided 1.0 Comp.Ex. 5 Not used Provided 0.3

1. A solution for buffer layer formation, for use in the step of formingan electroluminescent layer comprising a buffer layer and a luminescentlayer by patterning using a photolithographic process, said solution forbuffer layer formation comprising at least a metal oxide or aphotocatalyst and a heat- and/or photo-curable binder, said bindercomprising an organopolysiloxane that is a hydrolyzed condensate orcohydrolyzed condensate of one or two or more silicon compoundsrepresented by formula Y_(n)SiX_((4-n)) wherein Y represents an alkyl,fluoroalkyl, vinyl, amino, phenyl, or epoxy group; X represents analkoxyl group or a halogen; and n is an integer of 0 to
 3. 2. Thesolution for buffer layer formation according to claim 1, wherein saidphotocatalyst is titanium dioxide.
 3. A solution for buffer layerformation, for use in the step of forming an electroluminescent layercomprising a buffer layer and a luminescent layer by patterning using aphotolithographic process, said solution for buffer layer formationcomprising: an organic material that contains a hydrophilic group in itsmolecule and is dissolvable or dispersible in water or an alcohol; and asilane coupling agent.
 4. The solution for buffer layer formationaccording to claim 3, wherein said organic material comprisespolystyrenesulfonic acid or a polystyrenesulfonic acid derivative, orpolythiophenesulfonic acid or a polythiophenesulfonic acid derivative.5. The solution for buffer layer formation according to claim 3, whereinsaid organic material is a salt of a poly-3,4-alkenedioxythiophene withpolystyrenesulfonic acid, or a derivative thereof.
 6. The solution forbuffer layer formation according to claim 3, wherein said silanecoupling agent is represented by formula

wherein X represents OR wherein R represents an alkyl group; Yrepresents an epoxy or acryloyl group; and n is an integer of 0 to
 2. 7.The solution for buffer layer formation according to claim 6, whereinsaid silane coupling agent contains a glycido or acryloyl group.
 8. Asolution for buffer layer formation, for use in the step of forming anelectroluminescent layer comprising a buffer layer and a luminescentlayer by patterning using a photolithographic process, said solution forbuffer layer formation comprising an organic material in which a part orall of hydrophilic groups are converted to oleophilic groups and a partor all of said oleophilic groups are returned to hydrophilic groups byusing heat or radiation energy.
 9. The solution for buffer layerformation according to claim 8, wherein said organic material comprisespolystyrenesulfonic acid or a polystyrenesulfonic acid derivative, orpolythiophenesulfonic acid or a polythiophenesulfonic acid derivative.10. The solution for buffer layer formation according to claim 8,wherein said organic material is a salt of apoly-3,4-alkenedioxythiophene with polystyrenesulfonic acid, or aderivative thereof.